1. Field of the Invention
The invention relates to a straight motorized handpiece which is designed for medical purposes, preferably for use in a medical or dental laboratory.
A handpiece of the kind concerned is in particular suitable for that kind of mechanical work on natural or artificial parts of the human or animal body for which a comparatively large drive and working power is required. In the medical field such a handpiece is thus particularly suitable for work on comparatively solid parts of the body. In the dental field such a handpiece may be used for dental treatment in the oral cavity of a patient, if it is of correspondingly small construction.
A handpiece of the kind concerned is preferably suited for a medical, in particular dental laboratory, in which in particular artificial body parts or models are machined by means of rotary tools which can be clamped into the handpiece. The handpiece is suitable for the transmission of a comparatively large working power to the tool, and different tools may rapidly and readily be mounted or released and exchanged.
2. Discussion of the Prior Art
An important problem with a motorized handpiece of the kind concerned is that in particular the forward roller bearing becomes contaminated as a result of the penetration of dirt from the working area into the motorized handpiece and its service life is thus reduced through wear and tear. This applies in particular in the event that the motorized handpiece is used for working, in particular abrading, ceramics or metal, whereby the removed residue of the material being worked, in particular dust, finds its through the forward end of the motorized handpiece to forward bearing and penetrates into the bearing. Such demands on the motorized handpiece occur in particular during its use in medical or dental laboratories.
Another cause of penetration of contaminating substances into the forward bearing of the motorized handpiece results from the common measure of blowing out the forward end of the motorized handpiece with compressed air, for effecting the necessary cleaning of the handpiece, whereby the material residue reaches the bearing by means of the compressed air.
In order to protect the bearing, a sealing system has already been developed which is installed in front of the bearing. Such a handpiece, of the kind mentioned in the introduction, is marketed by the assignee under the designation K9-Handpiece Type 950 and is thus known. In the following this handpiece will be described with reference to FIG. 5.
The rod-shaped straight handpiece 1 comprises a rearward motor part 2, which is only partly illustrated, with an in particular electrical drive motor 3 mounted therein, and a forward handpiece part 4 into which, from the front, a working tool can be mounted with its shaft 5. For this purpose there serves a sleeve-like, slotted clamping chuck 6, which is part of a drive shaft 7, which is rotatably mounted coaxially in the handpiece part 4 and is connected with the drive motor 3 for rotation. The clamping chuck 6 can be opened and closed by means of a relative rotation between the motor part 2 and a grip sleeve 4a of the handpiece part 4. For this purpose an actuating mechanism 8 is integrated into the handpiece part 4, which mechanism is effective between the grip sleeve 4a and the drive shaft 7 and has a transmission 9 which converts the rotary movement of the grip sleeve 4a into an axial movement of a round draw rod 10, which extends from the rear coaxially through a bearing sleeve 7a of the drive shaft 7, is mounted therein axially displaceably in a bore and is screwed into an internal thread 6a of the clamping chuck 6 with its forward end. The grip sleeve 4a is mounted on a sleeve-like internal casing 11 to be rotatable around the longitudinal middle axis 12 of the handpiece 1 and to be longitudinally displaceable. In the internal casing 11, the drive shaft 7 is rotatably mounted by means of two roller bearings 13, 14 which have an axial spacing from one another, of which the forward roller bearing 14 bears against an internal annular shoulder 15 of the internal casing 11 with its rear side, whereby the outer ring of the roller bearing 14 is fixedly screwed against the internal ring shoulder 15 by a nut 16. The nut 16 is screwed into an internal thread at the forward end of the internal casing 11. Further, a front cap 47 is screwed into the internal thread in front of the nut 16, which cap covers the clamping chuck 6 approximately half of which projects from the internal casing 11.
With this known motorized handpiece 1 a sealing system 21 comprising several members is arranged before the forward roller bearing 14, into which system the nut 16 is integrated as part of the sealing system 21. The sealing system 21 comprises two sealing disks 22, 23, which are arranged at an axial spacing from one another and are effective between the nut 16 and an additional sealing surface ring 24, which is pushed tightly onto the sleeve-like section of the bearing shaft 7 immediately before the roller bearing 14 contacting the forward side of the roller bearing, which ring also carries the roller bearing 14. The sealing surface ring 24 has a radially projecting flange 25 on its rear end, which forms a sealing surface 26 on its forward side. The section of the sealing surface ring 24 which projects forwardly from the flange 25 is formed with a second cylindrical sealing surface 26a which is formed by the circumferential surface. The first sealing disk 22 sits fixedly in an internal groove 28 of the nut 16, and rests against the sealing surface 26 of the flange 25 with its rear side. The second sealing surface 23 bears against the forward side of the nut 16, whereby it glides on the sealing surface 26a and is held by a clamping ring 29 in the form of a so-called "Quad ring" in its functional position. The internal groove 28 is formed by an internal ring 31 which is emplaced in the nut 16 and fixed thereto.
This known configuration is complicated and has many elements and is thus expensive to manufacture. Furthermore substantial outlay in terms of installation effort and time is required to mount or de-mount the known sealing system Further, the known sealing system is of comparatively large constructional size, which also results in a larger constructional size of the motorized handpiece.
A further disadvantage of the known sealing system is to be perceived in that with a displacement of the clamping ring 29--which, possibly under the effect of compressed air, cannot be excluded--the second sealing disk 23 may be pressed with varying force, whereby either its sealing function is impaired, so that a deterioration of the seal must be reckoned with, or its glide seating may be affected in the sense of a firmer seating so that, in operation, considerable heating and wear have to be reckoned with.